A LED driving apparatus and a LED illumination system using the same are provided. The LED driving apparatus adapted to drive a LED load having at least one power specification includes a driving circuit, an output detecting circuit and an output adjusting circuit. The driving circuit provides an adjustable output current for driving the LED load. The output detecting circuit is coupled to the driving circuit and the LED load for detecting a driving voltage of the LED load to generate a first detecting signal. The driving circuit drives the LED load under a constant current in response to the first detecting signal. The output adjusting circuit is coupled to the output detecting circuit. The output adjusting circuit is controlled to adjust a signal level of the first detecting signal, such that the adjustable output current has at least one current adjusting range.